The state Board of Education revoked a contract with NCS Pearson in closed session Friday, after the Pearson PLC unit told officials it used the wrong table to score U.S. history exams for students on track to graduate this spring. Students who did poorly got overly high scores, while those who did better didn’t get enough credit.

Associate Superintendent Paula Vanderford says it’s too soon to know how many students may have graduated or been denied diplomas in error, or what the state will do about either circumstance.

Pearson spokeswoman Laura Howe apologized on behalf of the company and said Pearson is working to correct the scores.

“We are disappointed by today’s board decision but stand ready to assist the state in any way possible,” she wrote in an email.

Students typically study U.S. history in their third year in high school, and take the subject test that spring. Students who score poorly, though, can take the test up to three more times as a senior. The 951 students in questions were either seniors, or juniors scheduled to graduate early, and needed their scores to earn diplomas.

The answers about graduating students will be tricky because students have different options to graduate. Formerly, every student had to pass each of Mississippi’s four subject tests in biology, history, algebra and English to earn a high school diploma. Now, students can fail a test and still graduate if class grades are high enough, they score well enough on other subject tests, they score above 17 on part of the ACT college test, or earn a C or better in a college class. Eventually, the tests will count for 25 percent of the grades in each subject

About 27,000 students took the test overall. Vanderford said scores for each one will have to be verified. The exam scores also affect the grades that Mississippi gives to public schools and districts.

“The agency is committed to ensuring that the data is correct,” she said.

Vanderford said Pearson has had other problems with its Mississippi tests. In 2012, a scoring error on the high school biology exam wrongly denied diplomas to five students. Pearson compensated them with $50,000 scholarships to any Mississippi university. Another 116 student who were affected less severely got $10,000 or $1,000 scholarships. In 2015, Pearson paid the state $250,000 after its online testing platform crashed for a day.

Pearson had a contract worth a projected $24 million over the next six years to provide tests for history, high school biology, 5th grade science and 8th grade science. The board hired Minnesota-based Questar Assessment to administer all those tests for one year for $2.2 million. Questar, which is being bought by nonprofit testing giant ETS, already runs all of Mississippi’s language arts and math tests. Because Mississippi owns the questions to the history and science tests, Vanderford said it will be possible for Questar to administer those exams on short notice. The state will seek a contractor to give those tests on a long-term basis in coming months.